Continuously regenerated and integrated suppressor and detector for suppressed ion chromatography and method

ABSTRACT

An integrated suppressor and detector for suppressed ion chromatography includes a stationary phase, a fluid flow path, at least first and second regeneration electrodes, and at least first and second sensor electrodes. Methods of suppressed ion chromatography using the integrated suppressor and detector are also described.

FIELD OF THE INVENTION

The present invention relates to the field of ion chromatography (IC),and, in particular, to a continuously regenerated, integrated suppressorand detector for use in suppressed ion chromatography (SIC).

BACKGROUND OF THE INVENTION

Suppressed ion chromatography (SIC) is a commonly practiced method ofion chromatography which generally uses two ion-exchange columns inseries followed by a flow through conductivity detector for detectingsample ions. The first column, called the analytical or separationcolumn, separates the analyte ions in a sample by elution of the analyteions through the column. The analyte ions are flowed through theanalytical column via a mobile phase comprising electrolyte. Generally,a dilute acid or base in deionized water is used as the mobile phase.From the analytical column, the separated analyte ions and mobile phaseare then flowed to the second column, which is called the suppressor orstripper. The suppressor serves two primary purposes: (1) it lowers thebackground conductance of the mobile phase by retaining (e.g.,suppressing) the electrolyte of the mobile phase, and (2) it enhancesthe conductance of the analyte ions by converting the analyte ions totheir relatively more conductive acid (in anion analysis) or base (incation analysis). The combination of these two functions enhances thesignal to noise ratio, and, thus, improves the detection of the analyteions in the detector. Accordingly, upon exiting the suppressor, theanalyte ions and suppressed mobile phase are then flowed to the detectorfor detection of the analyte ions. A variety of different types ofsuppressor devices and methods are discussed in U.S. Pat. Nos.3,897,213; 3,920,397; 3,925,019; 3,926,559; and U.S. Ser. No.08/911,847. Applicants hereby incorporate by reference the entiredisclosure of these patent applications and patents.

As those skilled in the art will appreciate, both the mobile phase andthe sample contain counterions of the analyte ions. A suppressoroperates by ion exchange of suppressor ions, which are located in thesuppressor, with both the (1) the mobile phase electrolyte counterionsand (2) the sample counterions. In anion analysis, for example, thesuppressor ions normally comprise hydronium ions and the mobile phasecomprises electrolyte such as sodium hydroxide or mixtures of sodiumcarbonate and sodium bicarbonate. In cation analysis, the suppressorions normally comprise hydroxide ions, and the mobile phase may compriseelectrolytes such as hydrochloric acid or methanesulfonic acid. Thesuppressor ions are located on a stationary phase, which may be an ionexchange membrane or resin. As the mobile phase and sample (whichcontains both analyte ions and counterions of the analyte ions) areflowed through the stationary phase of the suppressor, the electrolytecounterions in the mobile phase and the sample counterions are retainedon the stationary phase by ion exchange with the suppressor ions. Whenthe suppressor ions are either hydronium or hydroxide, ion exchange ofthe electrolyte counterions with suppressor ions converts the mobilephase to water or carbonic acid, which are relatively non-conductive. Onthe other hand, the ion exchange of sample counterions with suppressorions (i.e., hydronium or hydroxide ions) converts the analyte ions totheir relatively more conductive acid (in anion analysis) or base (incation analysis). Thus, the analyte ions, which are now in theirrelatively more conductive acid or base form, are more sensitive todetection against the less conductive background of the mobile phase.

However, unless the suppressor ions are continuously replenished duringthe suppression process, the concentration of suppressor ions on thestationary phase is reduced. Eventually the suppressor will becomeexhausted and its suppression capacity is either lost completely orsignificantly reduced. Thus, the suppressor must be either replaced orregenerated. The need to replace or regenerate the suppressor isinconvenient, may require an interruption in sample analysis, or requirecomplex valving or regeneration techniques known in the art. One exampleof a known technique for regenerating a suppressor by continuouslyreplenishing suppressor ions is disclosed in U.S. Pat. No. 5,352,360.

In addition to the need for regenerating or replacing suppressor ions,another problem associated with SIC is that a separate suppressor unitis usually required, and, therefore, the number of components in thesystem is increased over traditional IC systems. Traditional IC systemsusually contain a mobile phase source, a pump, a sample injector, ananalytical column and a detector for detecting the sample ions. In SIC,a separate suppressor unit is added to the system. This, in turn,increases the complexity of the system and also increases extra-columnvolume which may decrease chromatographic resolution and sensitivity.Therefore, it would also be advantageous to have a system of ionsuppression chromatography which reduced the number of system componentsin traditional SIC systems.

Another problem associated with prior art SIC systems is that the mobilephase is converted to a weakly ionized form, which renders the mobilephase unsuitable for reuse. Thus, it would be advantageous if a systemof SIC were developed in which the mobile phase is converted back to itsstrongly ionized form after suppression and, thus, may be reused.

SUMMARY OF THE INVENTION

In its various aspects, the present invention is capable of solving oneor more of the foregoing problems associated with SIC.

In one aspect of the present invention, an integrated suppressor anddetector is provided. By “suppressor” it is meant a device that iscapable of converting the mobile phase to water or a weakly conductiveform such as, for example, sodium carbonate or bicarbonate to carbonicacid and the ions to be detected (e.g. the analyte ions) to either theiracid or base prior to detection. In this aspect of the invention, thesuppressor is further equipped with sensor electrodes for detecting theanalyte ions. By “integrated” it is meant that the suppressor anddetector are contained within the same housing so that fluid transferlines between a separately housed suppressor and detector areunnecessary.

In a further aspect of the invention, a method of suppression ionchromatography is provided wherein the suppressor is continuouslyregenerated during suppression. The suppressor comprises a stationaryphase comprising suppressor ions which acts to suppress a mobile phasecontaining analyte ions to be detected. Electrolysis is performed on themobile phase to produce regenerating ions. The regenerating ions arethen flowed through the stationary phase to continuously replenish thesuppressor ions lost during suppression. Preferably, electrolysis isperformed on water present in the mobile phase.

In another aspect of the invention, an integrated suppressor anddetector is provided. The integrated suppressor and detector comprisesat least first and second regeneration electrodes and a fluid flow pathextending between the first and second regeneration electrodes. Astationary phase comprising suppressor ions is positioned in the fluidflow path. The integrated suppressor and detector further comprises atleast first and second sensor electrodes, in an electrical communicationwith a measuring device for recording analyte ions detected by thesensor electrodes.

In yet another aspect of the invention, a method of suppression ionchromatography is provided wherein the suppressed mobile phase isconverted back to its strongly ionized state after suppression. Thus,the mobile phase is recycled and may be reused.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a suppressor ion chromatography systemincorporating the integrated suppressor and detector of the invention.

FIG. 2 is a cross-section view of integrated suppressor and detectoraccording to one aspect of the invention taken along line 2—2 of FIG.3a.

FIG. 3a is a side perspective view of an integrated suppressor anddetector according to one aspect of the invention.

FIG. 3b is a cross-section view taken along line B—B of FIG. 3a.

FIG. 4 is an exploded perspective view of an integrated suppressor anddetector according to another aspect of the invention.

FIG. 4a is a side view of an integrated suppressor and detector depictedin FIG. 4.

FIG. 4b is a cross-sectional view of an integrated suppressor anddetector.

FIGS. 5-7 are chromatograms using an apparatus and method according tothe invention and are referred to in the examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates an IC system using the integrated suppressor anddetector of the present invention. The IC system comprises a mobilephase source 10, a pump 11, a sample injector 12 and an analyticalcolumn 14, all in fluid communication. The pump 11, sample injector 12and analytical column 14 may be selected from the variety of types knownby those skilled in the art For example, preferred pumps include theALLTECH 526 pump available from ALLTECH ASSOCIATES, INC. (Deerfield,Ill.). Preferred analytical columns include the ALLTECH ALLSEP orUNIVERSAL CATION COLUMNS. Preferred sample injectors include theRHEODYNE 7725 injection valve.

An integrated suppressor and detector 16 in fluid communication with theanalytical column 14 is further provided. As discussed below, thesuppressor and detector 16 is connected to a power source 18 and ameasuring device 20. Preferred power sources include the KENWOODPR36-1.2A. A preferred measuring device is a conductivity detector suchas the OAKTON ¼ DIN Conductivity and Resistivity Controllers (OAKTON 100Series). Another suitable measuring device for use with the presentinvention is an electrochemical detector. The measuring device 20measures or records the analyte ions detected by sensor electrodes inthe integrated suppressor and detector 16.

In operation, the direction of fluid flow is as follows. The mobilephase is flowed from mobile phase source 10 by pump 11 through injectionvalve 12 to analytical column 14 to suppressor and detector 16. Uponexiting the suppressor and detector 16, the mobile phase is flowedthrough recycling valve 19, which directs fluid flow either to waste orback to mobile phase source 10 as discussed below. The recycling valve19 is preferably a three-way valve.

With reference to FIG. 2, the suppressor and detector 16 comprises afirst regeneration electrode 30 and a second regeneration electrode 32.The regeneration electrodes are held in housing 17 of the suppressor anddetector 16 by a threaded nut (not shown). Seals 241 and 241 a arepreferably included to provide a fluid-tight seal between electrodes 30and 32 and housing 17. The seals 241 and 241 a are preferably O-ringsmade from materials that are compatible with acids and bases such as,for example, ethylene propylene. Preferably, the regeneration electrodesare flow-through electrodes. By flow-through electrodes, it is meantthat the electrodes allow sample analyte ions and mobile phase to flowtherethrough. The electrodes are preferably made from carbon, platinum,titanium, stainless steel or any other suitable conductive, non-rustingmaterial. The most preferred electrodes are made of platinum coatedtitanium, ruthenium oxide coated titanium, titanium nitride coatedtitanium, gold, or rhodium with an average pore size of between 0.1 μmand 100 μm. The first regeneration electrode 30 and the secondregeneration electrode 32 are connected to the power source 18. A fluidflow path (indicated by arrows) is positioned between the first andsecond regeneration electrodes. The fluid flow path may preferablyextend from the first regeneration electrode 30 to the secondregeneration electrode 32. The fluid flow path may be defined byinternal walls of housing 17. Housing 17 is preferably made from aninert material such as those disclosed in co-pending application Ser.No. 08/911,847. Also, as those skilled in the art will appreciate, thehousing 17 should be constructed from a relatively non-conductivematerial.

A stationary phase 39 is positioned in the fluid flow path. Thestationary phase 39 may comprise a variety of stationary phases known inthe art for suppressors. Such stationary phases include membranes andion exchange resins, for example. Preferably, the stationary phasecomprises ion exchange resin. In anion analysis, cation exchange resinwill be used. A preferred cation exchange resin is BIORAD AMINEX 50W-X12(which is a sulfonated polystyrene divinylbenzene 200-400 mesh). Othersuitable stationary phases include DUPONT NAFION ion-exchange beads andmembranes and PUROLITE ion-exchange resins. During operation, thepreferred cation exchange resin comprises exchangeable hydronium ions.In cation analysis, anion exchange resin will be used. A preferred anionexchange resin is BIORAD AMINEX AG1-X8 100-200 mesh (which is aquaternary amine polystyrene divinyl benzene). During operation, thepreferred anion exchange resin comprises exchangeable hydroxide ions.

The suppressor and detector 16 also comprise at least two sensorelectrodes for detecting the analyte ions. In the present embodiment,two sensor electrodes, first sensor electrode 37 and second sensorelectrode 38 are shown. The first and second sensor electrodes arepreferably located in the fluid flow path between first regenerationelectrode 30 and second regeneration electrode 32. The first and secondsensor electrodes preferably comprise either platinum wire or anotherelectrochemically inert material such as gold, rheuthinium oxide orplatinum, either neat or plated or suitable substrates such as titaniumor stainless steel. The sensor electrodes 37 and 38 are preferably inelectrical communication with a measuring device (not shown) forrecording the analyte ions detected by the sensor electrodes. Withreference to FIGS. 3a and 3 b, the first and second sensor electrodespreferably have a serpentine configuration across a cross-section of theflow path. In particular, two rows of four holes each (see referencenumerals 40-43 and 44-47, respectively) are provided. The first sensorelectrode 37 is weaved through holes 40-43 and the second electrode 38is weaved through holes 44-47 formed in housing 17. Most preferably, atleast a portion of the stationary phase 39 will be positioned in thefluid flow path between the first and second sensor electrodes. Finally,an end of each of the first sensor electrode 37 and the second sensorelectrode 38 is in electrical communication with the measuring device20. Preferably, the suppressor and detector 16 is 21 mm×7.5 mm internaldiameter. In a preferred aspect of the invention, the distance betweenthe regeneration electrode 30 and sensor electrode is about 7.95 mm. Thedistance between regeneration electrode 32 and sensor electrode 38 isabout 11.8 mm. The distance between sensor electrodes 37 and 38 is about1.4 mm.

The system of the present invention may be used for detecting analyteions comprising anions or cations. Moreover, a variety of mobile phasesmay be used. For cation analysis, preferred mobile phases includeaqueous solutions of either hydrochloric acid, methanesulfonic acid orsulfuric acid. For anion analysis, preferred mobile phases includeaqueous solutions of either sodium hydroxide or sodiumcarbonate/bicarbonate. Preferably, the mobile phase is aqueous and,therefore, no separate water-source is required. The operation of thesuppressor and detector 16 will be described with reference to FIG. 2for anion analysis and a mobile phase consisting of an aqueous solutionof sodium hydroxide. As those of ordinary skill in the art will quicklyappreciate, the invention may easily be adapted for cation analysisalso.

To prepare the system for operation, the mobile phase should be flowedthrough the system and the power source turned on. Once the baselinecreated by the mobile phase has stabilized, the system is ready for ionanalysis. A sample, which contains analyte anions to be detected andanalyte counterions (e.g., cations), is injected at sample injector 12and flowed to analytical column 14 by pump 11. The analyte anions areseparated (or resolved) in analytical column 14 and then flowed with themobile phase to suppressor and detector 16.

In anion analysis, the stationary phase 39 in the suppressor anddetector 16 is preferably ion exchange resin comprising exchangeablehydronium ions. The sample which contains the previously separatedanalyte anions from analytical column 14 along with the analytecounter-cations are flowed with the mobile phase to the suppressor anddetector 16. The analyte counter-cations are retained on the stationaryphase 39 by ion exchange with the hydronium ions. Thus, the analyte ionsare converted to their relatively more conductive acid according to thefollowing formula:

I⁺X⁻+stationary phase−H⁺=HX+stationary phase−I⁺

(where X⁻ comprises analyte anions selected from, for example, Cl, NO₂,Br, etc.; and I⁺ are analyte counterions selected from, for example,K⁺). Also, the sodium ions in the mobile phase may be retained on thestationary phase 39 by ion exchange with the hydronium ions. Thus, themobile phase is converted to the relatively non-conductive wateraccording to the following formula:

NaOH+stationary phase−H⁺=H₂O+stationary phase−Na⁺

In addition to the foregoing reactions, a current is created acrossstationary phase 39, first regeneration electrode 30 and secondregeneration electrode 32 by power source 18. The water from the aqueousmobile phase undergoes electrolysis to form regenerating ions at thefirst regeneration electrode 30 and second regeneration electrode 32,respectively. In anion analysis, the first regeneration electrode 30 isthe anode at which regeneration ions consisting of hydronium ions aregenerated. The second regeneration electrode 32 is the cathode at whichhydroxide ions are generated. As those skilled in the art willrecognize, in cation analysis the polarity is reversed and the upstreamregeneration electrode will be the cathode and the regenerating ionswill comprise hydroxide ions.

In this embodiment, the regenerating hydronium ions generated at thefirst regeneration electrode 30 are then flowed through the stationaryphase 39 thereby continuously regenerating the stationary phase 39 byion exchange of the regenerating hydronium ions with the retained sodiumions and analyte counter-cations according to the following formulas:

H⁺+stationary phase−Na⁺=stationary phase−H⁺+Na⁺

H⁺+stationary phase−I⁺=stationary phase−H⁺+I⁺

The sodium ions released from the stationary phase 39 are flowed to thesecond regeneration electrode 32 where they combine with theregeneration hydroxide ions to yield aqueous sodium hydroxide. If thereare no analyte anions or analyte counter-cations flowing from thesuppressor and detector 16, this aqueous sodium hydroxide may be flowedthrough recycling valve 19 and back to mobile phase source 10. In thisfashion, a self-regenerating mobile phase is also provided. If, however,there are analyte anions or analyte counter-cations exiting thesuppressor and detector 16 along with the aqueous sodium hydroxide, thefluid flow is preferably directed to waste. Preferably, the system willinclude a solvent recycling device, such as the ALLTECH SOLVENT RECYCLER3000, which will sense the absence of analyte anions or analytecounter-cations and automatically direct the flow of the regeneratedsodium hydroxide mobile phase to source 10. In contrast, if the solventrecycling device detects the presence of sample ions or counter-ions, itwill direct the fluid flow to waste.

In a preferred embodiment of the invention, the analyte ions aredetected while in the suppressor and detector 16. Still with referenceto the anion analysis discussed above, there is a high concentration ofhydronium ions proximate to sensor electrodes 37 and 38. The source ofthese hydronium ions are the regeneration hydronium ions generated atfirst regeneration electrode 30 and the hydronium ions released from thestationary phase 39 by ion exchange with the sodium ions and analytecounter-cations. Preferably, the concentration of hydronium ions isgreater than the concentration of sodium ions or analyte counter-cationsproximate the sensor electrodes. By optimizing the concentration ofhydronium ions, the amount of sample ions in the acid form is likewiseoptimized, which leads to better detection sensitivity.

As discussed above, a current is applied across the stationary phase 39for generating the regeneration ions. When the analyte anions in theiracid form are flowed to the sensor electrodes, a change in the currentis detected by the sensor electrodes. This change in current, and theextent of the change, reflects the amount of analyte ion present in thesuppressor and detector 16. Preferably, the change in current isdetected by a measuring device 20 and recorded.

In an alternate embodiment of the invention (not shown), the separatesensor electrodes may be omitted and the first and second regenerationelectrodes 30 and 32 may also function as the sensor electrodes aspreviously described above. In yet another embodiment of the invention(not shown), one of the sensor electrodes may be omitted and one of theregeneration electrodes may perform the function of both a regenerationelectrode and a sensor electrode as discussed above.

Another aspect of the invention using an ion-permeable ion exchangemembrane is depicted in FIG. 4. FIG. 4 is an exploded view of analternative configuration for the suppressor and detector. Suppressorsusing ion exchange membranes having this general configuration (exceptfor the sensor electrodes) are known in the art. Examples of thesesuppressors are disclosed in U.S. Pat. Nos. 5,248,426 and 5,352,360, thedisclosure of which are hereby incorporated by reference. In theembodiment depicted in FIG. 4, a first regeneration electrode 130 and asecond regeneration electrode 132 are provided. The electrodes may beconstructed from the same materials as previously discussed. However, asthose of ordinary skill in the art will appreciate, the electrodes 130and 132 preferably are not flow-through electrodes in this embodiment.First and second ion exchange membranes 134 and 135 are also provided.First and second ion exchange membranes preferably comprise exchangeableions selected from the group consisting of hydronium and hydroxide ions.Positioned between ion exchanged membranes 134 and 135 and electrodes130 and 132 are a first set of spacers 130 a and 132 a, which definefluid flow paths providing fluid communication between electrode 130 andmembrane 134 and electrode 132 and membrane 135, respectively. Also,adjacent first and second ion exchange membranes are second set ofspacers 140 and 141, respectively, which define a fluid flow path 145.The spacers 130 a, 132 a, 140 and 141 preferably may comprise apermeable, inert material such as a TEFLON membrane. Alternatively, thespacers may comprise an inert sheet constructed from MYLAR, PTFE,polypropylene or the like which has been cut to provide fluidcommunication between membranes 134 and 135 and the fluid flow path 145as well as between electrodes 130 and 132 and membranes 134 and 135,respectively. Positioned in spacers 140 and 141 are sensor electrodes137 and 138, respectively, which may be as previously described.Preferably, the sensor electrodes 137 and 138 are positioned at thedownstream end of fluid flow path 145. As those skilled in the art willappreciate, the sensor electrodes will be positioned so that they are influid communication with the fluid flow path 145. Also, in theconfiguration depicted in FIG. 4, in addition to fluid flow path 145,fluid flow paths 145 a and 145 b are defined by the combination ofspacer 130 a and membrane 134 and spacer 132 a and membrane 135,respectively.

In operation, the suppressor and detector depicted in FIG. 4 operatesalong the same general principles as previously discussed with respectto the embodiment depicted in FIGS. 1-3b. However, whereas the directionof current flow is generally parallel to the direction of fluid flow inthe embodiment depicted in FIGS. 1-3b, the direction of current flow isgenerally perpendicular to the direction of fluid flow in the embodimentdepicted in FIG. 4. Thus, in anion analysis, for example, the samplecomprising analyte ions (anions) and sample counterions along with anaqueous mobile phase comprising electrolyte counterions are flowed tosuppressor and detector 116 and fluid flow path 145. The water in themobile phase undergoes electrolysis. In this embodiment, electrode 130may be the anode and electrode 132 may be the cathode. Thus, hydroniumions are generated at electrode 130 and hydroxide ions are generated atthe electrode 132. As the analyte ions and mobile phase are flowedthrough fluid flow path 145, the analyte counterions and mobile phaseelectrolyte counterions are retained on the membranes 134 and 135 by ionexchange with hydronium ions. The hydronium ions, both from themembranes 134 and 135 and the electrolysis product of water, migrate tofluid flow path 145 converting the analyte ions to their acid and themobile phase to water. The analyte anions in their acid form may then bedetected by sensor electrodes 137 and 138.

Additionally, the hydronium ions from the electrolysis will replace theretained electrolyte and sample counterions on membranes 134 and 135thereby regenerating these membranes. The released electrolytecounterions may then recombine with the hydroxide ions generated by theelectrolysis at electrode 132 to regenerate the mobile phase, which maybe reused as described previously.

Although the sensor electrodes 137 and 138 may be positioned in one ofthe fluid flow paths 145, 145 a or 145 b, preferably, the sensorelectrodes will be placed in path 145. Also, the sensor electrodes 137and 138 are in electrical communication with a measuring device (notshown) for recording the detected analyte ions.

The devices and systems disclosed in U.S. Pat. Nos. 5,248,426 and5,352,360 may be adapted for use according to yet another aspect of theinvention. FIG. 4b shows a cross-section of a suppressor and detector316 having the configuration of the suppressor and detector depicted inFIG. 4, except that the path of fluid flow through the suppressor anddetector is modified. The electrodes 330 and 332, membranes 334 and 335and spacers 330 a, 332 a, 340 and 341 may be as described with respectto FIG. 4. The sensor electrodes 337 and 338 are positioned in the fluidflow path 345. Preferably, the sensor electrodes are positioned towardsthe downstream end of fluid flow path 345. However, in this embodiment,the path of fluid flow is through fluid flow path 345 and then backthrough fluid flow paths 345 a and 345 b in a direction of flow oppositethe direction of fluid flow through path 345.

With reference to FIG. 4b, in anion analysis, for example, an aqueousmobile phase comprising electrolyte is flowed through fluid flow path345 to fluid flow paths 345 a and 345 b A sample comprising analyteanions and analyte counterions is flowed through fluid flow path 345.The analyte counterions are retained on membranes 334 and 335 by ionexchange with hydronium ions. Similarly, the mobile phase electrolytesare retained on membranes 334 and 335 by ion exchange with hydroniumions. The released hydronium ions from membranes 334 and 335 and thehydronium ions generated at electrode 330 from the electrolysis of waterin the mobile phase combine with the analyte anions in the fluid flowpath 345 forming the acid of the analyte anions and converting themobile phase to water. The analyte anions, in their acid form, are thendetected in the fluid flow path 345 by sensor electrodes 337 and 338,which are preferably in electrical communication with a measuring device(not shown).

The analyte anions (in their acid form) and water is then flowed tofluid flow paths 345 a and 345 b. This provides a continuous supply ofwater for the electrolysis. Also, the continuous supply of hydroniumions generated at electrode 330 replaces the retained sample andelectrolyte counterions on membranes 334 and 335, thereby continuouslyregenerating these membranes. The displaced sample and electrolytecounterions (cations) migrate towards electrode 332 (where hydroxideions are generated by the electrolysis) to flow path 345 b and out ofsuppressor and detector 316. The effluent from flow paths 345 a and 345b may be flowed to waste.

As those skilled in the art will appreciate, one of the spacers 140 and141 (FIG. 4) or spacers 340 and 341 (FIG. 4b) may be eliminated. Thus,instead of two spacers, one spacer defining a fluid flow path 145 (FIG.4) or 345 (FIG. 4b) may be used.

EXAMPLE 1

In this example, sample anions were analyzed according to a method ofthe invention using a suppressor and detector according to theembodiment of FIG. 2. The following items were used. The analyticalcolumn was an ALLTECH ALLSEP anion column, 100×4.6 mm ID packed withmethacrylate-based quaternary amine anion exchange resin. The mobilephase was aqueous 0.7 mM sodium bicarbonate/1.2 mM sodium carbonate. Themobile phase flow rate was 0.5 mL/min. The integrated suppressor anddetector was packed with high capacity polystyrene divinylbenzene basedsulfonated cation exchange resin (BIORAD AMINEX 50W-X12 200-400 mesh).The integrated suppressor and detector was a column 21×7.5 mm ID. Thedistance between the inlet regenerating electrode and the first sensorelectrode was 7.95 mm. The distance between the second sensor electrodeand the outlet regenerating electrode was 11.8 mm. The distance betweenthe first and second sensor electrodes was 1.4 mm. The conductivitydetector was an OAKTON 1000 series ¼ DIN conductivity and resistivitycontroller. The power source was a KENWOOD PR 32-1.2 A regulated DCpower supply. The amount of current applied was 100 mA (correspondingvoltage of 15 V).

FIG. 5 is the chromatogram for a sample anion mixture (100 μL). Thefollowing peaks correspond to the following anions: 1—flouride (10 ppm);2—chloride (20 ppm); 3—nitrite (20 ppm); 4—bromide (20 ppm); 5—nitrate(20 ppm); 6—phosphate (30 ppm); and 7—sulfate (30 ppm).

EXAMPLE 2

In this example, the same equipment and conditions as in Example 1 wereused. FIG. 6 is the chromatogram for a sample anion mixture with threerepetitive injections of 100 μL each. The following peaks correspond tothe following anions: 1—chloride (10 ppm); and 2—sulfate (10 ppm).

EXAMPLE 3

In this example, sample cations were analyzed according to a method ofthe invention shown in the embodiment of FIG. 2. The following equipmentand conditions were used. The analytical column was an ALLTECH Universalcation column, 100×4.6 mm ID, packed with silica coated withpolybutadiene-maleic acid cation exchange resin. The mobile phase wasaqueous 3.0 mM methane sulfonic acid. The mobile phase flow rate was 0.5mL/min. The integrated suppressor and detector was packed withpolystyrene divinyl benzene quaternary amine resin (BIORAD AMINEXAG-1-X8 100-200 mesh). The integrated suppressor and detector had thedimensions as set forth in Example 1. The conductivity detector was anOAKTON 1000 series ¼ DIN conductivity and resistivity controllers. Acurrent of 200 mA was applied (corresponding voltage is 22 V).

FIG. 7 is a chromatogram for a sample cation mixture, 4 repetitiveinjections of 100μ mL each. The following peaks correspond to thefollowing cations: 1—lithium (1 ppm); 2—potassium (6 ppm); and3—magnesium (6 ppm).

It should be understood that the foregoing description of the preferredembodiments and the examples are not intended to limit the scope of theinvention. The invention is defined by the claims and any equivalents.

We claim:
 1. A method of detecting analyte ions in an aqueous mobilephase comprising electrolyte using continuous electrochemicalregeneration of a suppressor comprising: (a) separating the analyte ionsin a mobile phase comprising electrolyte; (b) flowing the separatedanalyte ions and mobile phase through a suppressor comprisingion-exchange resin through which the mobile phase and analyte ions areflowed thereby suppressing the mobile phase electrolyte and at leastpartially exhausting the suppressor ion-exchange resin; (c) flowing anaqueous liquid through the suppressor and applying an electricalpotential across the suppressor ion-exchange resin during step (b) toelectrolyze water and thereby generating regeneration ions selected fromthe group consisting of hydronium ions and hydroxide ions; (d) flowingthe regeneration ions through the at least partially exhaustedsuppressor ion exchange resin in substantially the same direction as thedirection of liquid flow through the suppressor ion exchange resinduring step (b): and (e) detecting the analyte ions.
 2. The method ofclaim 1 wherein the aqueous liquid comprises the aqueous mobile phase.3. The method of claim 1 wherein the analyte ions comprise anions andthe suppressor ion-exchange resin comprises hydronium ions.
 4. Themethod of claim 1 wherein the analyte ions comprise cations and thesuppressor ion-exchange resin comprises hydroxide ions.
 5. The method ofclaim 1 wherein the analyte ions are detected during step (b).
 6. Themethod of claim 5 wherein the analyte ions comprise cations and thesuppressor ion-exchange resin comprises anions.
 7. The method of claim 5wherein the analyte ions comprise anions and the suppressor ion-exchangeresin comprises cations.
 8. The method of claim 1 wherein theregeneration ions are flowed in substantially the same direction as thedirection of the separated analyte ion flow through the suppressor ionexchange resin.
 9. A method of detecting analyte ions in an aqueousmobile phase using continuous electrochemical regeneration of asuppressor comprising: (a) separating the analyte ions; (b) flowing theseparated analyte ions through a suppressor comprising ion-exchangeresin to suppress the mobile phase thereby at least partially exhaustingthe suppressor ion-exchange resin; (c) flowing an aqueous liquid throughthe suppressor and applying an electrical potential across thesuppressor ion-exchange resin during step (b) to electrolyze water andregenerate the at least partially exhausted suppressor ion-exchangeresin; and (d) detecting the analyte ions in the suppressor during step(b).
 10. The method of claim 9 wherein the analyte ions comprise anionsand the suppressor ion-exchange resin comprises hydronium ions.
 11. Themethod of claim 9 wherein the analyte ions comprise cations and thesuppressor ion-exchange resin comprises hydroxide ions.
 12. The methodof claim 9 wherein in step (c) regeneration ions selected from the groupconsisting of hydronium ions and hydroxide ions are generated by theelectrolysis of water, the regeneration ions being flowed across the atleast partially exhausted ion exchange resin in substantially the samedirection as the direction of liquid flow through the suppressor ionexchange resin.
 13. The method of claim 9 wherein in step (c)regeneration ions selected from the group consisting of hydronium ionsand hydroxide ions are generated by the electrolysis of water, theregeneration ions being flowed across the at least partially exhaustedion exchange resin in substantially the same direction as the directionof separated analyte ion flow through the suppressor ion exchange resin.14. A method of detecting analyte ions in an aqueous mobile phasecomprising electrolyte using continuous electrochemical regeneration ofa suppressor wherein the suppressor comprises a housing havingsuppressor ion exchange resin in direct contact with a pair ofelectrodes, the suppressor housing being a separate housing from ananalytical column, the method comprising: (a) separating the analyteions in a mobile phase comprising electrolyte; (b) flowing the separatedanalyte ions and mobile phase through the suppressor thereby suppressingthe mobile phase electrolyte and at least partially exhausting thesuppressor ion-exchange resin; (c) flowing an aqueous liquid through thesuppressor and applying an electrical potential across the suppressorion-exchange resin during step (b) to electrolyze water and therebygenerating regeneration ions selected from the group consisting ofhydronium ions and hydroxide ions; (d) flowing the regeneration ionsthrough the at least partially exhausted suppressor ion exchange resinduring step (b): and (e) detecting the analyte ions in substantially thesame direction as the direction of analyte ion flow through thesuppressor ion exchange resin.